In situ mining of fluids by heating the resource layer of a geologic formation was done extensively by Sweden in World War II to acquire oil during a shortage. Electrical resistance heaters were placed in boreholes often in hexagonal patterns to surround a vapor borehole. The resource layer is heated successively by applying current to several rows of heating elements at a time. As soon as the gas is removed from a section corresponding to a row of heating resistors, the current is applied to the next row. During wartime, the energy efficiency was not an issue, since embedded shale could be made to produce oil by means of available hydroelectric power.
Modern fuel cells are used downhole, but the purpose of these fuel cells is to produce electricity for pump operations. In the prior art, fuel cell stacks were constructed in discreet modules of a size tailored to their electrical demand or dictated by the compressive and other forces at work inside the stack.
These short stacks were then typically connected in arrays, which in aggregate produce the desired quantity of electrical energy.
U.S. patent application Publication No. US2002/0011 335A1(2002) to Zhang et al. discloses the use of downhole fuel cells to generate electricity for mining operations. Zhang at paragraph 0065,mentions the use of heat generated by the fuel cell to power devices, which presumably could include a hot water heater, and an unspecified use in highly viscous, cool environments. There are no known teachings of specifically designing a fuel cell assembly to heat a resource layer in an in situ mining operation.
There is a need for a subterranean heater with greater efficiency in terms of net energy production and reduced energy cost for mineral extraction and other applications. The heater would preferably consume a gaseous fuel of the type generated by the subterranean formation being heated as a normal by-product of the operation being performed to avoid the need to import fuel.
Ideally, the heater would produce heat uniformly along its length, without risk of autocombustion and would heat a formation at a reduced net cost for fuel. The present invention incorporates all of these advantages.
U.S. patent Pub. No. 2002/0011335 (Zhang) teaches the operation of down-hole fuel cells from down-hole “fuel and oxidant vessels”, page 2, ¶ 0038, (see Zhang, FIG. 1 , #12 & #14) also called “oxidant reservoirs” and “fuel reservoirs” page 7, ¶ 0083. According to Zhang, when said reservoirs “have exhausted their resources”, they are replenished from “external sources” like “bottles/tanks”, which are themselves types of reservoirs.
The present invention is unique, in part, in that the fuel cells, located in a borehole, are in physical communication with the planet surface through conduits. Said conduits serve as continuous passages for the movement of fluids-fuels, oxidants, and exhaust products—to and from the fuel cells.
The present invention is an improvement because fuel and oxidant can be supplied to the fuel cells continuously from the surface without the need to replenish down-hole reservoirs.
Geothermic Fuel Cells (GFC's) are unique in that they are designed to be linearly scalable. This is to say that GFC stacks are designed to be extensible, up to lengths of 1000 feet. This has been achieved by designing a fuel cell stack comprised of modular building blocks—modules that can be assembled end-to-end to create stacks of scalable length.